1. Field of the Invention
The present invention relates to a lithium ion secondary battery and a manufacturing method of the lithium ion secondary battery.
2. Description of the Related Art
The lithium ion secondary battery has a high energy density when compared with a nickel hydrogen battery and the like and is used, for example, as a power supply of mobile electronic devices. In recent years, the scope of application thereof is further increased to medium- to large-size uses such as an on-vehicle power supply of hybrid electric vehicles and electric vehicles, a stationary uninterruptible power supply, and a power smoothing power supply. For example, electric vehicles are demanded to achieve a longer traveling distance and to meet such a demand, still higher energy densities (higher capacities) of lithium ion secondary batteries are desired.
In recent years, a lithium ion secondary battery using a silicon (Si) alloy as a negative electrode active material is expected. The Si alloy is in a state in which fine particles of the metal silicon (Si) are dispersed in each particle of other metal elements or other metal elements are dispersed in each particle of Si. The other metal elements include at least one of aluminum (Al), nickel (Ni), copper (Cu), iron (Fe), titanium (Ti), and manganese (Mn). The service capacity of the Si alloy extremely higher than that of graphite, but the coefficient of cubic expansion when fully charged is about 200 to 300% and if no countermeasure is taken against this cubic expansion, the electrode may collapse and drop off with cycles and in addition to decreased capacities, the battery may be expanded and made unusable as a battery. Thus, how to limit the expansion is a big challenge to apply the Si alloy to the negative electrode.
As a technology to limit the expansion of the negative electrode, for example, JP-2005-293943-A discloses a nonaqueous electrolyte secondary battery including a negative electrode mixture layer containing composite particles made of a metal or a compound thereof capable of occluding and releasing lithium and an electron conducting material and characterized by 0.5<D50/T<1 when the particle size D50 (μm) of the composite particle in the total number 50% integrated in ascending order of particle size in an integrated distribution curve is set as the thickness T (μm) on one side of the negative electrode mixture layer. According to JP-2005-293943-A, the composite particle size containing the negative electrode active material is relatively large with respect to the thickness of the negative electrode mixture layer and the number of composite particles contained per unit volume of the negative electrode mixture layer can be decreased and, as a result, even if the volume of composite particles changes with charge and discharge cycles, the number of poor connection locations between composite particles and between composite particles and conductive agents is small and thus, a nonaqueous electrolyte secondary battery with a small expansion can be obtained.
JP-2006-253126-A discloses a negative electrode active material for a nonaqueous electrolyte secondary battery capable of electrochemically occluding and releasing Li, wherein an alloy material containing Si and at least one of Ti and Zr and a graphite material are included and the surface of the graphite material is covered with the alloy material. According to JP-2006-253126-A, the degradation of battery characteristics with the expansion of alloy material can be inhibited in a negative electrode using both the alloy material and the graphite material and therefore, a high-capacity nonaqueous electrolyte secondary battery with superior cycle characteristics can be realized.
JP-2010-108944-A discloses a nonaqueous secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode contains a lithium containing transition metal oxide, the negative electrode contains a compound containing Si atoms into/from which lithium can be inserted/released and further, the coefficient of expansion is accompanying lithium insertion of the negative electrode is 1.05 or more and 3.0 or less and the average particle size of the Si compound is 0.001 to 5 μm. According to JP-2010-108944-A, by using a Si compound of “ultrafine particles”, the coefficient of expansion of the negative electrode is made smaller and the cycle life is further improved.
WO-2013/027686-A discloses a manufacturing method of a composite active material for a lithium secondary battery, including a mixing step of obtaining a mixture by mixing graphite whose specific surface area is 30 m2/g or more and a battery active material capable of combining with lithium ions and a spheroidizing step of manufacturing a composite active material for a lithium secondary battery in a substantially spherical shape containing a battery active material capable of combining with graphite and lithium ions by providing spheroidization treatment to the mixture. According to WO-2013/027686-A, the contact frequency and adhesiveness between graphite and the battery active material are good and as a result, high electrical conductivity is provided to the battery active material and the loss of conductive path due to a particle collapse of the battery active material with charge and discharge cycles can be avoided and as a result, high cycle characteristics of a lithium secondary battery can be realized.
WO-2013/069197-A discloses a negative electrode material for a lithium ion secondary battery capable of occluding and releasing lithium ions and containing negative electrode active material particles made of an element capable of an alloying reaction with lithium and/or an element compound capable of an alloying reaction with lithium, wherein 85% or more by volume of the negative electrode active material particles have the particle size of 1 μm or more when the whole particles are set as 100% by volume, the BET specific surface area is 6 m2/g or less, and D50 of the negative electrode active material particles is 4.5 μm or more. Negative electrode active material particles made of the Si phase and the SiO2 phase might as well be formed by the SiO2 phase of negative electrode active material particles being made of SiO2 to absorb the expansion/contraction of the Si phase and the Si phase being coated with the SiO2 phase and one particle, that is, a negative electrode active material particle might as well be formed by a plurality of fine Si phases being coated with the SiO2 phase and integrated and in such a case, the volume change of whole negative electrode active material particles can effectively be inhibited.
WO-2013/054481-A discloses a lithium ion secondary battery including a positive electrode and a negative electrode having a negative electrode active material containing SiOx (0.5≤x≤1.5) and graphite, wherein the compounding ratio of SiOx is 27% to 51% by weight when the SiOx and the graphite are set as 100% by weight. According to WO-2013/054481-A, SiOx powder is arranged in voids formed by graphite powder and even if the SiOx powder expands, the SiOx powder and the graphite powder are rearranged so as not to expand in the thickness direction and therefore, even if the SiOx powder expands, the volume change in the thickness direction of the negative electrode is inhibited.
WO-2013/101921-A discloses a negative electrode for a lithium ion secondary battery including a current collector and an active material layer formed on the surface of the current collector, wherein the active material layer contains an active material, a binder, and a cushioning medium, the active material is made of SiOx (0.5≤x≤1.5) powder, the cushioning medium is made of graphite powder, D50 of the SiOx powder is ¼ to ½ of D50 of the graphite, the compounded quantity of the graphite powder is 36% to 61% by weight when the total of the weight of the graphite powder and that of the SiOx powder is set as 100% by weight, and the content of the binder is 5% to 25% by weight when the weight of the whole active material layer is set as 100% by weight. According to WO-2013/101921-A, a lithium ion secondary battery capable of inhibiting volume changes of the negative electrode can be developed.